<template>
  <div class="upload-excel">
    <div class="btn-upload">
      <el-button :loading="loading" size="mini" type="primary" @click="handleUpload">
        点击上传
      </el-button>
    </div>

    <input
      ref="excel-upload-input"
      class="excel-upload-input"
      type="file"
      accept=".xlsx, .xls"
      @change="handleClick"
    >
    <div class="drop" @drop="handleDrop" @dragover="handleDragover" @dragenter="handleDragover">
      <i class="el-icon-upload" />
      <span>将文件拖到此处</span>
    </div>
  </div>
</template>
<script>
import * as XLSX from 'xlsx'

export default {
  props: {
    beforeUpload: Function, // eslint-disable-line
    onSuccess: Function// eslint-disable-line
  },
  data() {
    return {
      loading: false,
      excelData: {
        header: null,
        results: null
      }
    }
  },
  methods: {
    generateData({ header, results }) {
      this.excelData.header = header
      this.excelData.results = results
      // 判断该组件在被使用的时候，是否传递了onSuccess属性，如果传了onSuccess方法，
      // 会在读取成功后，自动调用该方法，将读取结果返回出去
      this.onSuccess && this.onSuccess(this.excelData)
    },
    handleDrop(e) {
      e.stopPropagation()
      e.preventDefault()
      if (this.loading) return
      const files = e.dataTransfer.files
      if (files.length !== 1) {
        this.$message.error('Only support uploading one file!')
        return
      }
      const rawFile = files[0] // only use files[0]

      if (!this.isExcel(rawFile)) {
        this.$message.error('Only supports upload .xlsx, .xls, .csv suffix files')
        return false
      }
      this.upload(rawFile)
      e.stopPropagation()
      e.preventDefault()
    },
    handleDragover(e) {
      e.stopPropagation()
      e.preventDefault()
      e.dataTransfer.dropEffect = 'copy'
    },
    handleUpload() {
      // 模拟点击input文件选择框
      this.$refs['excel-upload-input'].click()
    },
    // 当选择了excel文件的时候
    handleClick(e) {
      // 获取文件对象
      const files = e.target.files
      const rawFile = files[0] // only use files[0]
      if (!rawFile) return
      // 如果文件存在，走解析逻辑
      this.upload(rawFile)
    },
    // 解析excel
    upload(rawFile) {
      // 清空文件选择框value值，避免选择相同的文件不触发change事件
      this.$refs['excel-upload-input'].value = null // fix can't select the same excel

      if (!this.beforeUpload) {
        // 如果使用该组件时候，没有传递一个beforeUpload方法进来，就直接读取文件
        this.readerData(rawFile)
        return
      }
      // 如果传递了beforeUpload方法，会调用这个方法，将文件对象抛出去
      const before = this.beforeUpload(rawFile)
      if (before) {
        this.readerData(rawFile)
      }
    },
    // 读取excel文件（利用XLSX插件来读取文件）
    readerData(rawFile) {
      this.loading = true
      return new Promise((resolve, reject) => {
        // 实例化一个读取文件对象
        const reader = new FileReader()
        reader.onload = e => {
          // 读取处理excel数据
          const data = e.target.result
          const workbook = XLSX.read(data, { type: 'array' })
          const firstSheetName = workbook.SheetNames[0]
          const worksheet = workbook.Sheets[firstSheetName]
          // 读取表头数据
          const header = this.getHeaderRow(worksheet)
          // 读取表体数据
          const results = XLSX.utils.sheet_to_json(worksheet)
          // 将读取的数据，返回
          this.generateData({ header, results })
          this.loading = false
          resolve()
        }
        reader.readAsArrayBuffer(rawFile)
      })
    },
    getHeaderRow(sheet) {
      const headers = []
      const range = XLSX.utils.decode_range(sheet['!ref'])
      let C
      const R = range.s.r
      /* start in the first row */
      for (C = range.s.c; C <= range.e.c; ++C) { /* walk every column in the range */
        const cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })]
        /* find the cell in the first row */
        let hdr = 'UNKNOWN ' + C // <-- replace with your desired default
        if (cell && cell.t) hdr = XLSX.utils.format_cell(cell)
        headers.push(hdr)
      }
      return headers
    },
    isExcel(file) {
      return /\.(xlsx|xls|csv)$/.test(file.name)
    }
  }
}
</script>
<style scoped lang="scss">
.upload-excel {
  display: flex;
  justify-content: center;
   margin-top: 100px;
   .excel-upload-input{
       display: none;
        z-index: -9999;
     }
   .btn-upload , .drop{
      border: 1px dashed #bbb;
      width: 350px;
      height: 160px;
      text-align: center;
      line-height: 160px;
   }
   .drop{
       line-height: 80px;
       color: #bbb;
      i {
        font-size: 60px;
        display: block;
      }
   }
}
</style>
